The way a lot of people do it is to set up a target at 25 meters, set the rear sight on the "1" (100 meters) setting and sight in point of aim-point of impact.
This makes it easy to get on the paper without having hits off the target at 100 meters.
Then without moving the sight, sight in at 100 meters to insure you're hitting the target center.
Once set, you can shoot at any range by moving the sight to that distance, OR set the rear sight on the battle sight setting, which is the upside down "U" position and be able to hit a man at any range out to 400 meters.
The advantage here is that the marks on the sight are valid for different ranges but you still have a battle sight setting that doesn't require changing the sight.
Remember, the sight is in meters, and you need as close as you can get to a true 25 meter and 100 meter range.